Fiber-reinforced composites structures are used in a variety of automotive, aerospace and like industries where strong and durable, but lightweight, products and components are desirable. In general, these products are manufactured by blending reinforcing fibers with plastic materials, forming the mixture into a desired shape, and then consolidating the plastic materials into a solid matrix encompassing the reinforcing fibers. The reinforcing fibers provide substantial strength to the composite product.
There are a number of different methods and materials which are successfully used to form composite products. One such method involves the use of a blended tow of thermoplastic, or matrix, fibers and reinforcing fibers, such as carbon fibers. The tow, which is a loose, bundle of continuous fibers, both thermoplastic and reinforcing fibers, is formed into the shape of the desired product, for example, by winding the tow around a mandrel or by placing the tow into a shaped cavity, or by like methods- The entire structure is then heated in order to melt the thermoplastic fibers. The melted thermoplastic polymer then forms a matrix which surrounds and is reinforced by the reinforcing fibers.
The use of intimately admixed tows of reinforcing fibers and thermoplastic fibers for the preparation of composite articles and the preparation of such intimately admixed tows are disclosed, for example, in: SJA Slater; Research Disclosure 20239, February 1991; and in Baucom, Robert, NASA Tech. Brief, Fall, 1982, page 98. Similarly, British Patent 1,200,342 to Davis discloses various processes for forming blends of matrix and reinforcing fibers in order to provide an intimately mixed blend prior to heating thereof- Such processes include carding, extrusion of two materials simultaneously so that the extrudates intermesh, feeding continuous fibers side-by-side to form abatt or mat and/or winding continuous reinforcing and matrix fibers together.
U.S. Pat. Nos. 4,874,563; 4,871,491; 4,818,318; and 4,799,985, all to McMahon, et al. disclose methods for preparing composite fiber blends wherein separately provided tows of thermoplastic fibers and reinforcing fibers are uniformly spread and thereafter the uniformly spread tows are brought into contact with each other and intimately admixed together. According to these patents, good wetting of the reinforcing fibers by the thermoplastic material is obtained when appropriate heat and pressure are applied to the mixed tow because of the substantially uniform distribution of the thermoplastic fibers and the reinforcing fibers within the fiber blend.
Although intimately admixed and uniformly blended mixtures of reinforcing fibers and thermoplastic matrix fibers are capable of producing high quality composite products, the various process steps and process control necessary to ensure the formation of a blend having both types of fibers uniformly distributed throughout the blend can increase the complexity of the processes for preparing the blends and/or the manufacturing cost associated therewith.